Exemplary embodiments of the present invention relate to a packet combining device and method for a communication system using hybrid automatic repeat request (HARQ).
As the communication system develops and information to be transmitted contains multimedia information, it becomes more important to transmit information quickly and effectively. However, an information loss may be caused by noise, fading, or interference occurring in a communication channel. In order to effectively overcome an error caused by the information loss, it is necessary to use error correction coding.
The error correction coding refers to a technology in which a transmitter adds a parity bit to an information bit to transmit, and effectively decodes bits received through a channel, thereby increasing the reliability of the information bit.
In order to overcome a channel error occurring in a digital communication system, an error correction technology using turbo codes has been first proposed by Claude Berrou, in 1993. An error correction ability of the turbo codes has a characteristic in which bit-error rate (BER) performance is improved according to a repeat number, and it is known that when a sufficient number of iterations are performed, error correction may be achieved around a channel capacity published by C. E. Shannon [refer to C. Berrou, A. Glavieux and P. Thitimajshima, “Near Shannon limit error correcting coding and decoding: turbo-codes,” ICC 1993, Geneva, Switzerland, pp. 1064-1070 May 1993.].
A basic decoder of a turbo decoder is implemented by using a MAP (Maximum A Posteriori) algorithm or SOVA (Soft Output Viterbi Algorithm).
The MAP algorithm known as a BCJR algorithm was used as a basic decoding algorithm of a turbo decoder which has been first published by Claude Berrou [BCJR algorithm has been disclosed in L. R. Bahl, J. Cocke, F. Jelinek and J. Raviv, “Optimal decoding of linear codes for minimizing symbol error rate,” IEEE Transactions on Information Theory, Vol IT-20, pp 284-287, March 1974.].
Furthermore, the SOVA has been proposed by J. Hagenauer [refer to J. Hagenauer, “A Viterbi algorithm with soft-decision outputs and its application”, Proc. GLOBECOM'89 Dallas, Tex., pp 47.1.1-47.1.7, November 1989.], and the architecture of a turbo decoder using the SOVA as a basic decoder has been published by Berrou [refer to C. Berrou, P. Adde, E. Angui and S. Faudeil “A low complexity soft-output Viterbi decoder” ICC 1993, Geneva, Switzerland, pp 737-740, May 1993.].
In general, it is known that a turbo decoder using the MAP algorithm is two to four times more complex than a turbo decoder using the SOVA in terms of computational complexity, and is more excellent by 0.5 dB to 0.7 dB in terms of performance. Meanwhile, the architecture of a turbo decoder using a modified Log-MAP algorithm, which is obtain by simplifying a Log-MAP algorithm to facilitate hardware implementation, has been published by S. S. Pietrobon [refer to S. S. Pietrobon and S. A. Barbulescu, “A simplification of the modified Bahl decoding algorithm for systematic convolutional codes,” ISITA 1994, Sydney, NSW, pp 1073-1077, November 1994.]. Furthermore, since the existing Log-MAP algorithm is difficult to implement, Sub-Log-MAP and Max-Log-MAP algorithms have also been published to reduce a computational amount while accepting a performance reduction.
The turbo codes have been adopted to perform error correction for high-speed data transmission requiring a low BER in the LTE (Long Term Evolution) standard which is a next-generation mobile communication system as well as the current mobile communication system, and adopted as the error correction standard of a digital broadcasting communication system.
In general, a turbo decoder calculates only a log likelihood ratio (LLR) of a systematic part. Referring to FIG. 1, however, U.S. Pat. No. 6,307,901 of Motorola has disclosed a technical idea in which a turbo decoder computing an LLR of a parity bit is used to feedback the LLR, thereby improving the performance of the turbo decoder.
The HARQ scheme is an advanced form of the ARQ scheme and is a method of attempting a retransmission to reduce an error and loss of a packet. In the HARQ, the information of previously-transmitted packets is utilized to retransmit a packet, in order to increase the reliability of the retransmitted packet.
The HARQ scheme may be divided into a chase combining (CC) scheme and an incremental redundancy (IR) scheme.
The CC scheme utilizes both signal information of a retransmitted packet and previously-transmitted packets. At this time, an initially-transmitted original packet is transmitted as the retransmitted packet. That is, since the original packet and the retransmitted packet are combined to attempt reception, a unique combining effect of the HARQ scheme may be obtained.
Furthermore, the IR scheme uses a coding scheme such as turbo codes, rate compatible punctured convolutional (RCPC) codes, or low density parity check (LDPC) codes. In the IR scheme, information which is to be transmitted by a transmitter is coded to generate a redundancy information block, only an original packet excluding redundancy information is transmitted at the initial transmission, and the redundancy information block is transmitted instead of the entire original packet, when the transmission fails. That is, the redundancy information generated by the coding is transmitted for a retransmission request of the IR scheme, instead of the original packet. At this time, a receiver receives only the original packet at the initial transmission, and attempts reception by combining the original packet and the retransmitted packets when the redundancy block is received for the retransmission request. Therefore, a unique combining effect of the HARQ scheme and a coding gain may be obtained.
However, when the HARQ scheme is performed according to the conventional schemes, data obtained by combining previously-received data and newly-received data is inputted to a channel decoder. In this case, although the unique combining effect of the HARQ and the coding gain are obtained, the data improved by the channel decoder cannot be used.
Therefore, there is demand for a method of using the high-quality data improved by the channel decoder.
The related art of the present invention has been disclosed in U.S. Pat. No. 6,307,901 (2001 Oct. 23).